System for generating power from a syngas fermentation process

ABSTRACT

A system and process is provided for generating power from a syngas fermentation process. The process includes contacting hot syngas having a temperature above about 1400° F. with cooled syngas to produce a pre-cooled syngas having a temperature of 1400° F. or less at an inlet of a waste heat boiler. A waste heat boiler receives the pre-cooled syngas and is effective for producing waste heat boiler high pressure steam and a cooled syngas.

This application claims the benefit of U.S. Provisional Application Nos. 61/516,667, 61/516,704 and 61/516,646, all of which were filed on Apr. 6, 2011, and all of which are incorporated in their entirety herein by reference.

A system and process is provided for generating power from a syngas fermentation process. More specifically, a process is provided for generating high pressure steam from gasification and fermentation of syngas.

BACKGROUND

Microorganisms can produce ethanol and other compounds from carbon monoxide (CO) through fermentation of gaseous substrates. The CO is often provided to the fermentation as part of a gaseous substrate in the form of a syngas. Gasification of carbonaceous materials to produce producer gas or synthesis gas or syngas that includes carbon monoxide and hydrogen is well known in the art. Typically, such a gasification process involves a partial oxidation or starved-air oxidation of carbonaceous material in which a sub-stoichiometric amount of oxygen is supplied to the gasification process to promote production of carbon monoxide.

Syngas produced by gasification processes described in the art can be hot and needs cooling prior to downstream processing and subsequent fermentation. Hot syngas comprising carbon monoxide generated in a gasification apparatus, is cooled in a heat exchanger or waste heat boiler downstream of the gasification apparatus, see for example U.S. Pat. Nos. 6,435,139; 7,587,995 and 7,552,701. Recovery and use of this heat content of hot syngas can be very important for process economics.

SUMMARY

A process and system are provided that effectively generate high pressure steam from a syngas fermentation process. The process includes contacting hot syngas having a temperature above about 1400° F. with cooled syngas to produce a pre-cooled syngas having a temperature of 1400° F. or less at an inlet of a waste heat boiler. A waste heat boiler receives the pre-cooled syngas and is effective for producing waste heat boiler high pressure steam and a cooled syngas.

A system is provided for generating high pressure steam from a syngas fermentation process. The system includes a waste heat boiler positioned to receive syngas having a temperature of 1400° F. or less. The waste heat boiler effective for producing waste heat boiler high pressure steam and cooled syngas. A vent gas burner receives lean syngas from a fermentor and the vent gas burner is effective for producing hot vent gas burner gas. A vent gas boiler superheater receives the hot vent gas burner gas and the vent gas boiler superheater is effective for producing vent gas boiler high pressure steam. A steam mixer receives and mixes the waste heat boiler high pressure steam and the vent gas boiler high pressure steam to produce a combined high pressure steam.

In another aspect, a process is provided for generating high pressure steam from a syngas fermentation process. The process includes combusting carbonaceous materials in a gasifier to form a hot syngas having a temperature above about 1400° F. and pre-cooling the syngas to produce a pre-cooled syngas having an average temperature of 1400° F. or less at an inlet of a waste heat boiler. A waste heat boiler receives the pre-cooled syngas and is effective for producing waste heat boiler high pressure steam and a cooled syngas. A fermentor receives cooled syngas. A vent gas burner receives lean syngas from an outlet of the fermentor and the vent gas burner is effective for producing hot vent gas boiler gas. A vent gas boiler superheater receives the hot vent gas burner gas and waste heat boiler high pressure steam and produces a combined high pressure steam.

BRIEF DESCRIPTION OF FIGURES

The above and other aspects, features and advantages of several aspects of the process will be more apparent from the following drawings.

FIG. 1 is a general overview of a system that includes a waste heat boiler and vent gas boiler.

FIG. 2A and FIG. 2B illustrate an alternative aspect of a waste heat boiler system.

FIG. 3 illustrates an alternative aspect of a vent gas boiler system.

FIG. 4 is a general overview of another aspect of a system that includes a waste heat boiler and vent gas boiler.

Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various aspects of the present process and apparatus. Also, common but well-understood elements that are useful or necessary in commercially feasible aspects are often not depicted in order to facilitate a less obstructed view of these various aspects.

DETAILED DESCRIPTION

The following description is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles of exemplary embodiments. The scope of the invention should be determined with reference to the claims.

The process and system described herein effectively convert heat generated during gasification and fermentation of syngas into high pressure steam for generation of electrical power. The methods and system provide an excess of electrical power over what is needed for the overall system.

Definitions

Unless otherwise defined, the following terms as used throughout this specification for the present disclosure are defined as follows and can include either the singular or plural forms of definitions below defined:

The term “about” modifying any amount refers to the variation in that amount encountered in real world conditions, e.g., in the lab, pilot plant, or production facility. For example, an amount of an ingredient or measurement employed in a mixture or quantity when modified by “about” includes the variation and degree of care typically employed in measuring in an experimental condition in production plant or lab. For example, the amount of a component of a product when modified by “about” includes the variation between batches in a multiple experiments in the plant or lab and the variation inherent in the analytical method. Whether or not modified by “about,” the amounts include equivalents to those amounts. Any quantity stated herein and modified by “about” can also be employed in the present disclosure as the amount not modified by “about”.

“Carbonaceous material” as used herein refers to carbon rich material such as coal, and petrochemicals. However, in this specification, carbonaceous material includes any carbon material whether in solid, liquid, gas, or plasma state. Among the numerous items that can be considered carbonaceous material, the present disclosure contemplates: carbonaceous material, carbonaceous liquid product, carbonaceous industrial liquid recycle, carbonaceous municipal solid waste (MSW or msw), carbonaceous urban waste, carbonaceous agricultural material, carbonaceous forestry material, carbonaceous wood waste, carbonaceous construction material, carbonaceous vegetative material, carbonaceous industrial waste, carbonaceous fermentation waste, carbonaceous petrochemical co products, carbonaceous alcohol production co-products, carbonaceous coal, tires, plastics, waste plastic, coke oven tar, fibersoft, lignin, black liquor, polymers, waste polymers, polyethylene terephthalate (PETA), polystyrene (PS), sewage sludge, animal waste, crop residues, energy crops, forest processing residues, wood processing residues, livestock wastes, poultry wastes, food processing residues, fermentative process wastes, ethanol co-products, spent grain, spent microorganisms, or their combinations.

The term “fibersoft” or “Fibersoft” or “fibrosoft” or “fibrousoft” means a type of carbonaceous material that is produced as a result of softening and concentration of various substances; in an example carbonaceous material is produced via steam autoclaving of various substances. In another example, the fibersoft can include steam autoclaving of municipal, industrial, commercial, and medical waste resulting in a fibrous mushy material.

The term “municipal solid waste” or “MSW” or “msw” means waste that may include household, commercial, industrial and/or residual waste.

The term “syngas” or “synthesis gas” means synthesis gas which is the name given to a gas mixture that contains varying amounts of carbon monoxide and hydrogen. Examples of production methods include steam reforming of natural gas or hydrocarbons to produce hydrogen, the gasification of coal and in some types of waste-to-energy gasification facilities. The name comes from their use as intermediates in creating synthetic natural gas (SNG) and for producing ammonia or methanol. Syngas is combustible and is often used as a fuel source or as an intermediate for the production of other chemicals.

In one aspect, gasification of carbonaceous materials provides syngas. Gasification involves partial combustion of biomass in a restricted supply of oxygen. The resultant gas includes CO and H₂. In this aspect, syngas will contain at least about 20 mole % CO, in one aspect, about 20 to about 100 mole % CO, in another aspect, about 30 to about 90 mole % CO, in another aspect, about 40 to about 80 mole % CO, and in another aspect, about 50 to about 70 mole % CO. The syngas will have a CO/CO₂ ratio of at least about 0.75. Ser. Nos. 61/516,667, 61/516,704 and 61/516,646 describe some examples of suitable gasification methods and apparatus (U.S. Ser. Nos. 61/516,667, 61/516,704 and 61/516,646, all of which were filed on Apr. 6, 2011, and all of which are incorporated herein by reference). Syngas leaving the gasifier will have a temperature above about 1400° F., and in another aspect, at least about 1400° F. to about 3500° F. The gasification process is effective for destruction of tars.

The terms “fermentation”, fermentation process” or “fermentation reaction” and the like are intended to encompass both the growth phase and product biosynthesis phase of the process. In one aspect, fermentation refers to conversion of CO to alcohol.

High Pressure Steam System

FIG. 1 illustrates a system for generating high pressure steam. As shown in FIG. 1, the process and system provide a blended sygnas 120 by blending hot syngas 110 leaving a gasifier (not shown) with recycled cooled syngas. Recycled cooled syngas 140 contacts hot syngas 110 after leaving the gasifier. The recycled cooled syngas 140 contacts the hot syngas 110 at a point after the hot syngas leaves the gasifier and before the blended syngas 120 enters the waste heat boiler 100. In this aspect, the recycled cooled syngas 140 has a temperature of about 350° F. to about 450° F. A conduit or pipe transfers the recycled cooled syngas 140 to the hot syngas 110. Transfer of the recycled cooled sygnas 140 provides a ratio of recycled cooled syngas 140 to hot syngas of about 0.1 to about 20. In other aspect, ratios of recycled cooled syngas to hot syngas may include about 1 to about 15, about 1 to about 10, about 1 to about 5, about 1 to about 4, about 1 to about 3, about 1 to about 2, and about 1 to about 1.

The blended syngas 120 has an average temperature of about 1400° F. or less, in another aspect, about 600° F. to about 1400° F., in another aspect, about 750° F. to about 1400° F., in another aspect, about 600° F. to about 1400° F., in another aspect, about 750° F. to about 1200° F., in another aspect, about 750° F. to about 900° F., in another aspect, about 750° F. to about 825° F., and in another aspect, about 600° F. to about 900° F. The blended syngas 120 reaches these temperatures prior to entering the waste heat boiler 100. In this aspect, a thermocouple measures temperature at an inlet to the waste heat boiler prior to entering the waste heat boiler 100. The thermocouple may be positioned at any position across a diameter of the inlet.

As used herein, “average temperature” can be determined using known methods utilized to determine multiple temperatures across a diameter and then express those multiple temperature measurements as an average. In one aspect, computer modeling (including CFD) may be used to provide an average temperature. In other aspects, multiple temperature measurements may be made using temperature sensors such as thermocouples, infrared, radar, and the like.

As further shown in FIG. 1, the process and system provides blended syngas 120 to a waste heat boiler 100. The waste heat boiler 100 may be any know type of waste heat boiler effective for providing heat transfer from the blended syngas 120. In this aspect, the waste heat boiler 100 receives water/steam 160 and the waste heat boiler is effective for providing cooled sygnas 130 and waste heat boiler high pressure steam 170. In this aspect, the waste heat boiler high pressure steam 170 has a pressure of about 50 psig to about 950 psig. The process and system includes recycling 140 a portion of the cooled syngas 130 from the waste heat boiler 100 to the hot syngas 110. A fermentor receives cooled syngas 130 that is not recycled 150.

A vent gas burner 200 receives lean syngas 210 or off gas from a fermentor. The lean syngas 210 will typically have a CO/CO₂ ratio of less than about 1.0, in another aspect, about 0.01 to about 1.0, in another aspect, about 0.01 to about 0.5, and in another aspect, about 0.01 to about 0.1. The lean syngas may have higher concentrations of CO in the event of lower CO conversions in the fermentor. In this aspect, the lean syngas 210 or off gas may have a CO/CO₂ ratio of more than about 0.1. The vent gas burner 200 burns the lean syngas 210. Transfer of air 220 to the vent gas burner 200 may enhance combustion. Vent gas burners 200 may include any of those known in the art. The vent gas burner 200 provides a hot vent gas burner gas 230. In this aspect, the vent gas burner gas has a temperature of about 1500° F. to about 3000° F.

A vent gas boiler superheater 300 receives hot vent gas burner gas 230. Vent gas boiler superheaters may include any of those known in the art. The vent gas boiler superheater 300 receives water/steam 310 and the vent gas boiler superheater 300 provides a cooled vent gas boiler gas 320 and vent gas boiler high pressure steam 330. In this aspect, the vent gas boiler high pressure steam 330 has a pressure of about 600 psig to about 950 psig, and in another aspect, about 875 psig to about 925 psig. The vent gas boiler high pressure steam 330 and the waste heat boiler high pressure steam 170 are combined in a steam blender 180. The steam blender 180 provides a combined high pressure steam 400 having a pressure of about 600 psig to about 950 psig, and in another aspect, about 875 psig to about 925 psig. The combined high pressure steam 400 is utilized for production of power. Examples of equipment which may be utilized to produce power from high pressure steam include those known in the art, for example, steam turbines. In this aspect, increasing steam pressure from about 600 psig to about 900 psig will result in a net power gain.

In another aspect, the system may include steam drums (not shown) between the waste heat boiler 100 and steam blender 180, and between the vent gas boiler superheater 300 and steam blender 180.

An alternative configuration of a waste heat boiler is shown in FIG. 2A. This aspect includes both a waste heat boiler 100 and a waste heat boiler preheater 101 (also referred to as an economizer). As shown in FIG. 2A, the process and system provide a blended syngas 120 by blending hot syngas 110 leaving a gasifier (not shown) with recycled cooled syngas 140. As described herein, gasification of carbonaceous materials may provide sygnas. Syngas will contain at least about 20 mole % CO, and will have a temperature above about 1400° F. The waste heat boiler 100 provides a semicooled syngas 125. In this aspect, the semicooled syngas 125 has a temperature of about 500° F. to about 750° F.

A waste heat boiler preheater 101 receives the semicooled syngas 125. The waste heat boiler preheater 101 receives water/steam 160 and provides cooled syngas 130 and preheated water/steam 165. The process and system includes recycling 140 a portion of the cooled syngas 130 from the waste heat boiler preheater 101 to the hot syngas 110. A fermentor receives cooled syngas 130 that is not recycled 150. The waste heat boiler 100 receives the preheated water/steam 165 from the waste heat boiler preheater 101. The waste heat boiler 100 is effective for providing cooled sygnas 130 and waste heat boiler high pressure steam 170.

In another aspect as shown in FIG. 2B, the process and system includes recycling a portion of the semicooled syngas 125 from the waste heat boiler 100 to the hot syngas 110. The waste heat boiler preheater 101 receives a portion of the semicooled sygnas that is not recycled 126. In another aspect, the configuration s shown in FIGS. 2A and 2B may include steam drums (not shown). A steam drum may be positioned to receive preheated water/steam 165.

FIG. 3 illustrates an alternative configuration of a vent gas boiler superheater system. In this aspect, a vent gas boiler superheater 300 receives hot vent gas burner gas 230. The vent gas boiler superheater 300 receives preheated steam 312 and provides vent gas boiler high pressure steam 330 and semicooled vent gas boiler gas 322. In this aspect, vent gas boiler high pressure steam 330 has a pressure of about 600 psig to about 950 psig, and the semicooled vent gas boiler gas 322 has a temperature of from about 2000° F. to about 2500° F. In one aspect, a vent gas boiler steam generator 301 receives the semicooled vent gas boiler gas 322. The vent gas boiler steam generator 301 receives preheated water/steam 311 and provides preheated steam 312 and semicooled vent gas boiler gas 321. In another aspect, a vent gas boiler feed water preheater 302 receives the semicooled vent gas boiler gas 321. The vent gas boiler feed water preheater 302 receives water/steam 310 and provides preheated water/steam 311 and cooled vent gas boiler gas 320. In another aspect, the configuration shown in FIG. 3 may include a steam drum (not shown) positioned to receive preheated steam 331 and may provide water/steam 310.

FIG. 4 illustrates another aspect of a system for generating high pressure steam. As shown in FIG. 4, a vent gas boiler superheater 300 receives hot vent gas burner gas 230. The vent gas boiler superheater 300 receives preheated steam 312 and provides vent gas boiler high pressure steam 330 and semicooled vent gas boiler gas 322. In this aspect, the preheated steam 312 is provided by blending waste heat boiler high pressure steam 170 with preheated steam 331 from the vent gas boiler steam generator. The resulting vent gas boiler high pressure steam 330 has a pressure of about 600 psig to about 950 psig. The configuration shown in FIG. 4 may also include a steam drum (not shown) positioned to receive preheated steam 331.

In one aspect, the vent gas burner gas has a temperature of about 1500° F. to about 3000° F. The vent gas boiler superheater 300 also receives waste heat boiler high pressure steam 170. The vent gas boiler superheater 300 receives water/steam 310 and the vent gas boiler superheater 300 provides a cooled vent gas boiler gas 320 and a combined high pressure steam 400 having a pressure of about 600 psig to about 950 psig. The combined high pressure steam 400 is utilized for production of power. In this aspect, mixing waste heat boiler steam with vent gas boiler steam prior to superheating instead of mixing the waste heat boiler steam after the vent boiler steam is already superheated will result in a net power gain.

EXAMPLES Example 1: Effect of Syngas Cooler Inlet Temperature on Heat Transfer and Fouling

A gasifier having the design described herein was operated with the temperatures and flow rates described below. A fouling factor was determined as indicated.

Fouling factor at 600° F. inlet temperature to the syngas cooler:

Temperature of Syngas at Syngas Fouling Inlet of Feed Rate Factor Accumulated Syngas to Cooler Btu/ Time (hrs) Cooler (° F.) (lb/hr) (ft²h° F.) 7.7 601 477 0.022 15.7 614 512 0.034 23.7 597 862 0.009 31.7 608 730 0.008 40 605 1647 0.002 56 597 432 0.023 64.7 593 705 0.011 72 577 618 0.014 80 595 596 0.019 89 577 1416 0.007 188.15 583 355 0.006 196 572 372 0.024 207.7 565 345 0.048 216 577 317 0.034 223.7 572 385 0.024

Average fouling factor at 600° F. inlet was 0.019 Btu/(ft²h° F.).

A gasifier having the design described herein was operated with lower syngas cooler inlet temperatures and flow rates described below. A fouling factor was determined as indicated.

Fouling factor at 1300° F. inlet temperature to the syngas cooler:

Temperature of Syngas at Syngas Fouling Inlet of Feed Rate Factor Accumulated Syngas to Cooler Btu/ Time (hrs) Cooler (° F.) (lb/hr) (ft²h° F.) 7.5 1297 288 0.042 19.5 1293 314 0.070 105.5 1295 215 0.119 118.5 1295 230 0.100 129.5 1294 194 0.123 153.5 1297 191 0.098 166.5 1295 198 0.096 177.5 1295 233 0.072 190.5 1297 209 0.099 260.5 1308 240 0.050 273.5 1302 214 0.067 285.5 1301 183 0.082 298.5 1295 229 0.078 309.5 1296 264 0.080 317 1314 240 0.097 326.5 1328 275 0.078 338.83 1322 291 0.068 346.5 1332 281 0.070 350.5 1346 312 0.071 368.5 1336 213 0.081 374.5 1335 263 0.074

Average fouling factor at 1300° F. inlet was 0.078 Btu/(ft²h° F.).

While the invention herein disclosed has been described by means of specific embodiments, examples and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims. 

1-12. (canceled)
 13. A system for generating high pressure steam from a syngas fermentation process, the system comprising: a waste heat boiler positioned to receive syngas having a temperature of 1400° F. or less, the waste heat boiler effective for producing waste heat boiler high pressure steam and cooled syngas; a vent gas burner positioned to receive lean syngas from a fermentor, the vent gas burner effective for producing hot vent gas burner gas; a vent gas boiler superheater positioned to receive the hot vent gas burner gas, the vent gas boiler superheater effective for producing vent gas boiler high pressure steam; and a steam mixer positioned to receive and mix the waste heat boiler high pressure steam and the vent gas boiler high pressure steam to produce a combined high pressure steam.
 14. The system of claim 13 wherein the blended syngas has a temperature of about 600° F. to about 1400° F. at an inlet of the waste heat boiler.
 15. The system of claim 14 wherein the blended syngas has a temperature of about 600° F. to about 900° F.
 16. The system of claim 13 wherein the waste heat boiler high pressure steam has a pressure of about 50 psig to about 950 psig.
 17. The system of claim 13 wherein the vent gas boiler gas has a temperature of about 1500° F. to about 3000° F.
 18. The system of claim 13 wherein the vent gas boiler high pressure steam has a pressure of about 600 psig to about 950 psig.
 19. The system of claim 13 wherein the combined high pressure steam has a pressure of about 600 psig to about 950 psig.
 20. The system of claim 13 wherein the combined high pressure steam is utilized for production of power. 21-30. (canceled) 